Transcript for Pope Francis Meets With Argentine President Cristina Kirchner

And at the vatican today, the new pope sat down with a former adversary. The first head of state he met with. A woman, who once called his views medieval. A woman who won a victory over his fierce opposition. And tonight, abc's ron claiborne shows us the meeting between the pope and the president of argentina. Reporter: On one side, the new hugely popular pope. On the other, his old nemesis, the president of his native argentina. Today, they sat together like old friends. Cristina kirchner stands for a new view of a changing world -- embracing gay marriage, sex education in schools, free contraceptives in hospitals. But when he was a cardinal in argentina, kirchner described his social views as medieval. With his humble words and informal style, pope francis has become enormously popular in just a few days. What the world is just beginning to learn is how conservative he is on social issues. The world is probably going to have a bit of a wakeup call, when the pope starts speaking about hot button issues. Reporter: He often clashed with kirchner over legalizing gay marriage, calling it, "the devil's handiwork." He called gay adoption "discrimination against children," and he's denounced abor as promoting a "culture of death." But the powerful catholic strongholds of argentina and brazil are becoming more progressive. Gay marriage is now legal, contraception readily available. Threatening to put the popular new pope on a collision course with changing opinions in a part of the world where the church needs to grow. Ron claiborne, abc news, rome. And we want you to know that abc news will have leave coverage of the inaugural ceremony of pope francis tomorrow, about 3:50 a.M. Eastern time.

This transcript has been automatically generated and may not be 100% accurate.